Signals Intelligence (SIGINT): The NSA specialises in SIGINT, which involves the interception and analysis of signals to gather foreign intelligence and counterintelligence. This is a core function of the agency.
100 Mind-Blowing Interception Facts
Foreign Intelligence Surveillance Act (FISA): The 1978 FISA restricts the NSA’s mandate to the interception of foreign communications and forbids targeting U.S. citizens unless they are considered agents of a foreign power.